TIL that if you catch a home run ball from the visiting team at Wrigley Field you are expected to throw it back : r/todayilearned
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Throw it back
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For Cubs Fans, Enemy Home Runs Come With a Duty: 'Throw. It. Back.' - The New York Times
Why do Chicago Cubs fans throw the ball back? - Quora
Yankee fans: please stop throwing home run balls back onto the field - Pinstripe Alley
A Cubs fan on the street managed to toss a Cardinals home run all the way back into Wrigley